How to Use a GM TPI MegaSquirt Adapter Board

What does this board do?

Marc Piccioni’s new TPI adapter board works with 1986 to 1989 Corvettes, Firebirds, and Camaros with the TPI injection as a substitute for the “165” ECM; they are blue colored but otherwise very similar to the earlier TBI adapter board. These boards are meant to be used with Megasquirt-II only. In addition to the adapter board and Digikey parts, we currently recommend need a ‘747 ECM from a TBI truck for the mating connector and case. The ‘747 connector and internals are slightly different from the ‘165 ECM, which makes installing the adapter board easier, so we recommend using the 747 ECM as a donor ECU.

Assembling the TPI Adapter Board

Bill of materials:

Component

Description

Digi-Key Part Number

LS1, LS2

SPDT relay

255-2080-ND

R1, R4

1.0K resistor

1.0KQBK-ND

R3, R6

10K resistor

10KEBK-ND

R5

560R

560QBK-ND

D1

4.7V 500mW zener

1N5230BDICT-ND

D2

1N4001 diode

1N4001DICT-ND

Q1

TIP121

TIP121GOS-ND

Q2

2N3904

2N3904FS-ND

J1

DB37 female connector

A32129-ND or 182-837FE-ND

Disassemble the donor ECM and remove its harness connector using a “solder sucker” or solder wick.

Install R1 (1.0K resistor) and D1 (4.7 volt zener diode), taking care to install D1 with the banded end pointed towards the band on the PCB.

Install R3 (10K resistor) and R4 (1K resistor) if you are using this with an automatic transmission.

Install R5 (560 ohm resistor), and R6 (10K resistor).

Install D2 (1N4001 diode).

Install Q2, the 2N3904 transistor, if you are using this with an automatic transmission.

Install Q1, the TIP121 transistor. This one goes straight up and will bolt to case rail.

Step 50: You’ll be installing the ‘Hall/Optical Input Circuit’ (currently all steps under 50a). If you see any steps that say ‘only do this if you are triggering from the negative terminal of the coil’, you aren’t, so don’t.

Step 51: You don’t need these components, but I’d recommend installing them anyways.

Step 52: Set the jumpers for Hall/Optical/Points. That would be XG1 to XG2, OPTOIN to TACHSELECT, and TSEL to OPTOOUT.

Step 53: The adapter board gives you the option of using the GM MAP sensor instead of the one built into the Megasquirt. To do this, omit the MAP sensor and wire pin 1 of the MAP sensor header to the SPR3 pin.

Alternatively, you can use the Megasquirt’s MAP sensor for real time barometric correction. To do this, install the MAP sensor, but bend pin 1 so that it does not go into the hole (the hole will be jumpered to SPR3). Solder a 1K resistor to pin 1 of the MAP sensor, and solder a wire to the other end of the resistor. Cover this with heat shrink tubing, and run the other end of the wire to the JS5 pin. If you are using the sensor for barometric correction, do not connect any tubing to it.

Step 65: You will not be using the IGBT high current driver. Jumper JS10 to IGN to bring the signal out on pin 36.

To use the knock sensor input, run a jumper wire from JS4 to SPR4.

If you are using the automatic transmission lock-up control or shift light feature, run a jumper wire from SPR1 to pin 8 on the U1 40 pin socket. This will let you use the acceleration enrichment LED to control this.

If you’re using a DIYAutoTune.com MS230-C or MS2357-C MegaSquirt-II Assembled ECU:

Our assembled units are already set up for fuel and ignition control. There are several optional features you may want to use.

To use the stock GM MAP sensor and switch the built in MAP sensor to a barometric correction sensor, you’ll need to carefully desolder pin 1 of the MAP sensor. Jumper the resulting hole to SPR3. Solder a 1K resistor to pin 1 of the MAP sensor, and solder a wire to the other end of the resistor. Cover this with heat shrink tubing, and run the other end of the wire to the JS5 pin. If you are using the sensor for barometric correction, do not connect any tubing to it.

To use the knock sensor input, run a jumper wire from JS4 to SPR4.

If you are using the automatic transmission lock-up control or shift light feature, run a jumper wire from SPR1 to pin 8 on the U1 40 pin socket. This will let you use the acceleration enrichment LED to control this.

Fitting It in the Case

The TPI adapter board is designed to squeeze both the adapter and the Megasquirt into the stock case. The Megasquirt board is supported by the DB37 connector at one end and the other end is supported by the side rails.

Megatune Ignition Configuration:

Trigger offset = 10′ (this will vary, depending on the distributor orientation, see notes at the end of the article)

Ignition Input Capture to ‘Rising Edge’

Cranking Trigger to ‘Trigger Rise’

Coil Charging Scheme to ‘Standard Coil Charging’

Spark Output to ‘Going High (Inverted)’

Dwell is very low; try around 2 ms and adjust as needed.

More information on setting Trigger Offset:

You must also set the initial position of the trigger (called the ‘trigger offset’), then check it using the Trigger Wizard in MegaTune (Tools Menu). The trigger offset setting will vary according to your distributor position (where it is in rotation) but you’ll need to set it properly… Basically you use the Trigger Wizard and adjust the ‘trigger offset’ and/or twist your distributor until the advance number in the Trigger Wizard matches what you’re reading with your timing light. The +/- buttons on the trigger wizard will adjust your trigger offset. You’ll need to use these buttons and a timing light to make the number on your light, and the big number on the left in the Trigger Wizard, match up.

Here’s the information on this direct from the MegaTune Manual:

Before tuning your advance table, be sure to use a timing light to verify that your ‘trigger offset‘ is calibrated. Changing the Trigger Offset in MegaTune will not change the displayed advance, instead, it changes the actual advance as seen with a timing light. Your goal is to make these two match.

To do this, get your engine warmed-up (otherwise the timing moves as the temperature increases) and idling, then use a timing light to verify to be certain your actual advance as shown by a timing light equals your the advance display on the advance gauge in MegaTune. (8′ in this case). (Note that positive numbers denote BTDC, and negative numbers denote after TDC.)

Image courtesy of Bowling and Grippo

Cranking Timing Bypass

Some HEI modules – mostly aftermarket replacements – have a problems if you don’t turn off the bypass signal while the engine is cranking. TBI ECUs have a wire that sends the ECU a cranking signal. This automatic bypass feature is not present on the TPI ECUs, but the board has the parts to add this feature. If you are having problems losing spark while cranking, take the wire included with the adapter board and add it your harness connector on pin C9. Connect this to the ignition key on a terminal that gets 12 volts in the Start position but not the Run position. This will allow the bypass feature to function normally.

Spare outputs and inputs

The adapter board lets you control several features besides fuel and ignition. Two of these can be accessed through the spare port configuration screen in TunerStudio. The acceleration LED (PM4) now controls either the shift light or the torque converter lock-up. While the factory torque converter lock-up is controlled by the vehicle speed sensor (among other things), the MS-II does not have a vehicle speed sensor input. Instead, you can control it so that it is active above a certain RPM, and you can also set MAP reading or throttle position as a secondary condition. The FIDLE port controls the cooling fan.

For knock sensing, you can use the factory knock sensor on the engine.

The board does not control emissions devices like the EGR or canister purge.

If the end application is equipped with an automatic transmission that has a lock up torque converter, it is the end user’s responsibility to ensure that torque converter lock up does not occur in park, reverse, neutral or 1st gear. The transmission’s internal wiring should prevent the TCC from locking except in 4th gear, but if this wiring is damaged or modified, the adapter board will let you engage the lock up torque converter at any time.